1. Field of the Invention
This invention relates to a two stroke, multiple cylinder engine and more particularly to an improved two stroke, multiple cylinder engine most suitable to a small vehicle such as a snowmobile.
2. Description of Related Art
Snowmobiles are powered by internal combustion engines, particularly by two stroke, multiple cylinder engines. Usually, three cylinder engines are utilized because they allow easy choice of diameter for the cylinder bores without abnormal combustion despite having relatively large displacements. These engines have combustion chambers that are fired at intervals 120 degrees of crankshaft rotation angle relative to each other.
Preferably, an exhaust system for the engine has three separate exhaust conduits each allotted to a respective cylinder so as to utilize exhaust pulsation waves. Because the utilization of the exhaust pulsation waves is generally desirable for two stroke engines in progressing the charging efficiency of intake charges. That is, the negative pressure component of the exhaust pulsation wave contributes improvement of the delivery ratio that is one factor of the charging efficiency, while the positive pressure component of the same pulsation wave contributes improvement of the trapping efficiency of intake charges, that is another factor of the charging efficiency.
However, a snowmobile may allot relatively small and restricted space for components of the engine. Due to this restriction, usually such three separate exhaust conduits can not be accommodated. A single exhaust conduit is utilized instead of the three separate exhaust conduits. This single exhaust conduit can bring in lightening as well as minimization of the exhaust system and eventually those of the engine per se.
In the meantime, however, another problem arises in this arrangement. The aforenoted exhaust pulsation waves produced in each cylinder exert influence on the other cylinders. This influence is generally undesirable because the waveforms produced in other cylinders are different from the waveform that the certain cylinder requires and rather harmful. Particularly, the positive pressure component of the exhaust pulsation wave will prevent exhaust gasses from being discharged smoothly. Because of this, the charging efficiency of intake charges deteriorates and eventually invites deterioration in engine power and fuel efficiency.
It is, therefore, a principal object of this invention to provide an improved two stroke, multiple cylinder engine whereby minimization and lightening of an exhaust system will be realized without any deterioration in engine power and fuel efficiency.
It is another object to provide a two stroke, multiple cylinder engine whereby respective exhaust pulsation waves do not affect any undesirable influence on the other cylinders even though exhaust gasses are collected with a single exhaust conduit.
It is a further object to provide a two stroke, multiple cylinder engine whereby the positive pressure component of exhaust pulsation waves can be effectively removed or reduced.
In accordance with one aspect of this invention, a two stroke crankcase compression internal combustion engine has more than two combustion chambers for burning air fuel mixtures therein. A firing system is provided for firing the respective air fuel mixtures in the combustion chambers. An exhaust system is also provided for discharging exhaust gasses from the combustion chambers. The exhaust system has a single exhaust conduit collecting the exhaust gasses. The combustion chambers are unified to two groups. Respective combustion chambers belonging to the same group are fired generally simultaneously by means of the firing system.
In accordance with another aspect of this invention, a two stroke crankcase compression internal combustion engine has at least two combustion chambers for burning air fuel mixtures therein. A firing system is provided for firing the respective air fuel mixtures in the combustion chambers. An exhaust system is also provided for discharging the exhaust gasses from the combustion chambers. The exhaust system has a single exhaust conduit collecting the exhaust gasses. The combustion chambers are fired generally simultaneously by means of the firing system.
In accordance with a further aspect of this invention, a two stroke crankcase compression internal combustion engine has at least two combustion chambers for burning air fuel mixtures therein. An exhaust system is provided for discharging exhaust gasses from the combustion chambers. The exhaust system has a single exhaust conduit collecting the exhaust gasses. An attenuation mechanism is also provided for attenuating positive pressure reflection waves generated in the exhaust conduit.
In accordance with a still further aspect of this invention, a method is featured for firing a two stroke crankcase compression internal combustion engine. The engine has at least two combustion chambers for burning air fuel mixtures therein. An exhaust system is provided for discharging exhaust gasses from the combustion chambers. The exhaust system has a single exhaust conduit collecting the exhaust gasses. The method comprises the steps for firing some of the combustion chambers generally simultaneously and firing the rest of the combustion chambers generally simultaneously at a different timing relative to the firing at the fired group.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiments which follow.